Artificial gravity meeting zero gravity

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  • #26
DaveC426913
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As it turns out, the stress of a smaller, 3 rpm toroid maintaining 1 g is far less than that on a larger 1 rpm toroid maintaining the same 1 g. Less stress means less weight, less cost, and faster construction time for any given interior volume.
Well of course. This is always the case - more ambitious structures are more challenging and more demanding. If this weren't the case - if larger structures were not subject to more stresses etc., then we'd start low-tech by building large structures (like skyscrapers) and, as our technology improved our structures would get smaller (like bungalows) ... :eek:ne-eyebrow-cocked:

Instead, as is always the case, engineering effort is traded off in favour of end-usage of the structure (which is almost always larger=better).
 
  • #27
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Well of course. This is always the case - more ambitious structures are more challenging and more demanding. If this weren't the case - if larger structures were not subject to more stresses etc., then we'd start low-tech by building large structures (like skyscrapers) and, as our technology improved our structures would get smaller (like bungalows) ... :eek:ne-eyebrow-cocked:

Instead, as is always the case, engineering effort is traded off in favour of end-usage of the structure (which is almost always larger=better).
What if you factor in cost per unit area as well as long term maintenance costs? It might be that lots of simple and easy to maintain bungalows are more cost effective than big buildings. Plus, haven't you ever heard that the most urban growth in the 21st century will not occur in towering metal and glass but in user-fabricated shanty slums constructed of recycled building materials and scraps?
 
  • #28
DaveC426913
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But if the station didn't have windows, how would you even notice it was rotating except b/c of the AG?
The Coriolis Effects would be quite pronounced. You would feel yourself going in a circle.

But what happens first, the wings gaining lift or the bicycle tire slipping from lack of weight to create traction?
Well, lift of course will begin the moment you are moving, and ramp up from there, whereas traction will stay constant to a point then begin dropping rapidly to zero. So...
 
  • #29
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Why are the speeds actually even different? Isn't the G-force just a product of the momentum of the objects inside the station. So shouldn't any object move with 1G of force if it is accelerating at a given rate?
The *aapparent* artificial gravitational force has nothing to do with momentum of the objects inside thje station. It is actually centripetal force (what most people call centrifugal force) caused by the station's wall pushing up against your feet. If your motion was in a straight line (a tangent to the station's curve), there would be no upward force. But any given point on the station's wall is constantly being accelerated away from that straight line, toward the center, into a closed, circular curve. It is that acceleration that results in the force you would feel.

Dave
 
  • #30
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Toroids are preferred for a variety of reasons. The long cylinders envisioned by Gerard K. O'Neil aren't practical due to stablity reasons, and the greater the interior radius, the greater the stress on the pressure containment vessle. Toroids are also much easier to segment into separate pressure and fire containment areas. Without active stabilization, a cylinder will tumble, and the result would be catestrophiic. Multiple rotating toroids, on the other hand, can be linked to central non-rotating passageway at the axis. Care still needs to be taken, however, to disconnect precession forces between hubs, or you'll quickly wind up with an effective and unstable cylinder anyway.
Cylinders that aren't too spindly could be stabilized with tethers/booms at the periphery, and pairs of cylinders could be used. The instability's not a big enough issue to avoid the use of cylinders if they're otherwise more convenient.

Alternatively, you could have a high mass, slowly counterrotating outer shell...that provides a low gravity environment that would be useful for heavy machinery, takes mass off the high gravity inner section, allows for more shielding and machinery mass without adding to the structural mass required, provides a slow rotating outer shell that would be easier for spacecraft to rendezvous with, and lets you zero out the net angular momentum of the structure, eliminating the instability you mention.

For smaller structures, a habitat section and a counterweight linked by tethers allow a large radius of rotation without requiring a large monolithic structure.
 
  • #31
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Funny that these same calculations result in a counter-proof to the hollow-Earthers (Koreshian cosmogony):
If we did inhabit the inside surface of a hollow sphere the size of the Earth, the centripetal acceleration at the equator would be over 3G...
 
  • #32
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Funny that these same calculations result in a counter-proof to the hollow-Earthers (Koreshian cosmogony):
If we did inhabit the inside surface of a hollow sphere the size of the Earth, the centripetal acceleration at the equator would be over 3G...
So there is more force than just gravity holding the planet together?
 
  • #33
DaveC426913
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Funny that these same calculations result in a counter-proof to the hollow-Earthers (Koreshian cosmogony):
If we did inhabit the inside surface of a hollow sphere the size of the Earth, the centripetal acceleration at the equator would be over 3G...
How do you figure 3Gs?

If that were true, it would apply to the outer surface as much as the inner surface. What you are suggesting is that, standing on the outer surface of the Earth, I am experiencing a 3G pull away from the Earth!
 
  • #34
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How do you figure 3Gs?

If that were true, it would apply to the outer surface as much as the inner surface. What you are suggesting is that, standing on the outer surface of the Earth, I am experiencing a 3G pull away from the Earth!
Huh!! That would appear to be so! (Actually, 2G away, since the Earth's field is 1G inwards at the surface, vs. 0G inside a hollow shell.)

OK, here's how I got there:
a = v^2/r
Circumference of Earth is about 41,000 km, or 41e6 meters
Rotation is once in 86,400 seconds, for a tangential velocity of about 474 m/s.
Radius is about 6,500 km, which is where I went wrong - I divided by 6,500, not 6.5e6.
I got 34 m/s^2, should be 0.034 m/s^2

OK, so we're in no immediate danger of flying off into space!

Dave
 
  • #35
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A corollary to the above that I never thought of is that, even if the Earth were a perfect, homogeneous sphere, and ignoring the bulky clothes, I'd weigh nearly 5 pounds more at the poles than I do here at 37°N!
 
  • #36
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A corollary to the above that I never thought of is that, even if the Earth were a perfect, homogeneous sphere, and ignoring the bulky clothes, I'd weigh nearly 5 pounds more at the poles than I do here at 37°N!
So that's why Santa is so heavy.
 

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